Individual Junctions Research Articles

Intrinsic Josephson junction characteristics of Nd2-xCexCuO4 /SrTiO3 epitaxial films

The current-voltage (I-V) properties along the c axis on Nd2-xCexCuO4/SrTiO3 epitaxial films with x = 0.145, 0.15 were investigated. For all the samples it has been established that the I-V characteristics exhibit several resistive branches, which correspond to the resistive states of individual Josephson junctions. The results confirm the idea of a tunneling mechanism between the CuO2 layers (superconductor - insulator - superconductor junction) for the investigated Nd2-xCexCuO4 compound. The I-V dependence of this compound with x = 0.15 points out on the nonmonotonic nature of the d-wave or anisotropic s-wave symmetry order parameter associated with the coexistence of superconductivity and antiferromagnetic fluctuations.

Electrophysical cardiac remodeling at the molecular level: Insights into ryanodine receptor activation and calcium-induced calcium release from a stochastic explicit-particle model

We present the first-ever, fully discrete, stochastic model of triggered cardiac calcium dynamics. Using anatomically accurate subcellular cardiac myocyte geometries, we simulate the molecular players involved in calcium handling using high-resolution stochastic and explicit-particle methods at the level of an individual cardiac dyadic junction. Integrating data from multiple experimental sources, the model not only replicates the findings of traditional in silico studies and complements in vitro experimental data but also reveals new insights into the molecular mechanisms driving cardiac dysfunction under stress and disease conditions. We improve upon older, nondiscrete models using the same realistic geometry by incorporating molecular mechanisms for spontaneous, as well as triggered calcium-induced calcium release (CICR). Action potentials are used to activate L-type calcium channels, triggering CICR through ryanodine receptors (RyRs) on the surface of the sarcoplasmic reticulum. These improvements allow for the specific focus on the couplon: the structure-function relationship between L-type calcium channel and RyR. We investigate the electrophysical effects of normal and diseased action potentials on CICR and interrogate the effects of dyadic junction deformation through detubulation and orphaning of RyR. Our work demonstrates the importance of the electrophysical integrity of the calcium release unit on CICR fidelity, giving insights into the molecular basis of heart disease. Finally, we provide a unique, detailed, molecular view of the CICR process using advanced rendering techniques. This easy-to-use model comes complete with tutorials and all necessary software for use and analysis so as to maximize usability and reproducibility. Our work focuses on quantifying, qualifying, and visualizing the behavior of the molecular species that underlie the function and dysfunction of subcellular cardiomyocyte systems.

Flexible Crossbar Molecular Devices with Patterned EGaIn Top Electrodes for Integrated All-Molecule-Circuit Implementation.

Here, a unique crossbar architecture is designed and fabricated, incorporating vertically integrated self-assembled monolayers in electronic devices. This architecture is used to showcase 100 individual vertical molecular junctions on a single chip with a high yield of working junctions and high device uniformity. The study introduces a transfer approach for patterned liquid-metal eutectic alloy of gallium and indium top electrodes, enabling the creation of fully flexible molecular devices with electrical functionalities. The devices exhibit excellent charge transport performance, sustain a high rectification ratio (>103), and stable endurance and retention properties, even when the devices are significantly bent. Furthermore, Boolean logic gates, including OR and AND gates, as well as half-wave and full-wave rectifying circuits, are successfully implemented. The unique design of the flexible molecular device represents a significant step in harnessing the potential of molecular devices for high-density integration and possible molecule-based computing.

Large TRAPPC11 gene deletions as a cause of muscular dystrophy and their estimated genesis

BackgroundTransport protein particle (TRAPP) is a multiprotein complex that functions in localising proteins to the Golgi compartment. The TRAPPC11 subunit has been implicated in diseases affecting muscle, brain, eye and...

Dephasing in Fluxonium Qubits from Coherent Quantum Phase Slips

Phase slips occur across all Josephson junctions (JJs) at a rate that increases with the impedance of the junction. In superconducting qubits composed of JJ-array superinductors—such as fluxonium—phase slips in the array can lead to decoherence. In particular, phase-slip processes at the individual array junctions can coherently interfere, each with an Aharonov-Casher phase that depends on the offset charges of the array islands. These coherent quantum phase slips (CQPS) perturbatively modify the qubit frequency, and therefore charge noise on the array islands will lead to dephasing. By varying the impedance of the array junctions, we design a set of fluxonium qubits in which the expected phase-slip rate within the JJ array changes by several orders of magnitude. We characterize the coherence times of these qubits and demonstrate that the scaling of CQPS-induced dephasing rates agrees with our theoretical model. Furthermore, we perform noise spectroscopy of two qubits in regimes dominated by either CQPS or flux noise. We find that the noise power spectrum associated with CQPS dephasing appears to be featureless at low frequencies and not 1/f. Numerical simulations indicate that this behavior is consistent with charge noise generated by charge-parity fluctuations within the array. Our findings broadly inform JJ-array-design trade-offs, relevant for the numerous superconducting-qubit designs employing JJ-array superinductors. Published by the American Physical Society 2024

Non-Equilibrium Long-Wave Infrared HgCdTe Photodiodes: How the Exclusion and Extraction Junctions Work Separately.

The cooling requirement for long-wave infrared detectors still creates significant limitations to their functionality. The phenomenon of minority-carrier exclusion and extraction in narrow-gap semiconductors has been intensively studied for over three decades and used to increase the operating temperatures of devices. Decreasing free carrier concentrations below equilibrium values by a stationary non-equilibrium depletion of the device absorber leads to a suppression of Auger generation. In this paper, we focus on analyzing exclusion and extraction effects separately, based on experimental and theoretical results for a HgCdTe photodiode. To carry out an experiment, the n+-P+-π-N+ heterostructure was grown by metal organic chemical vapor deposition on CdTe-buffered GaAs substrate. In order to separate the extraction and exclusive junctions, three different devices were evaluated: (1) a detector etched through the entire n+-P+-π-N+ heterostructure, (2) a detector made of the P+-π photoconductive junction and (3) a detector made of the π-N+ photodiode junction. For each device, the dark current density-voltage characteristics were measured at a high-temperature range, from 195 K to 300 K. Next, the carrier concentration distribution across the entire heterostructure and individual junctions was calculated using the APSYS simulation program. It was shown that when the n+-P+-π-N+ photodiode is reverse biased, the electron concentration in the π absorber drops below its thermal equilibrium value, due to the exclusion effect at the P+-π junction and the extraction effect at the π-N+ junction. To maintain the charge neutrality, the hole concentration is also reduced below the equilibrium value and reaches the absorber doping level (NA), leading to the Auger generation rate's reduction by a factor of 2ni/NA, where ni is the intrinsic carrier concentration. Our experiment conducted for three separate detectors showed that the exclusion P+-π photoconductive junction has the most significant effect on the Auger suppression-the majority of the hole concentration drops to the doping level not only at the P+-π interface but also deep inside the π absorber.

Influence of Complex Geometries on Damage Tolerance of Porous Carbon Fiber Network

Porous materials exhibit a variety of attractive functional properties for aerospace applications, such as low density and low thermal conductivity. However, they must also be mechanically robust and damage tolerant to fully realize their potential. Currently, it is costly and time-consuming for testing under service conditions, therefore, computational models are a good path forward. Due to the inherent microstructural stochasticity of these structures, however, their behavior is difficult to effectively model without detailed experimental studies for validation and benchmarking. To that end this study investigates the mechanical properties of a porous carbon fiber network and ties together the global macroscopic observations to the local mesoscale behaviors dictated by individual fibers and fiber junctions. Strain localization was observed using digital image correlation (DIC) and tied to features within the macroscopic stress–strain plots. Work to quantify the impact of the addition of complex geometries (e.g., cracks and through-holes) on mechanical reliability was conducted. The defects resulted in distinct macroscale mechanical characteristics and mesoscale deformation behaviors, depending on defect type and loading orientation. These results provide broad experimental data to inform and validate modeling approaches to accurately predict and tailor the reliability of porous parts under service conditions.

Quantum Gas-Enabled Direct Mapping of Active Current Density in Percolating Networks of Nanowires.

Electrically percolating nanowire networks are among the most promising candidates for next-generation transparent electrodes. Scientific interest in these materials stems from their intrinsic current distribution heterogeneity, leading to phenomena like percolating pathway rerouting and localized self-heating, which can cause irreversible damage. Without an experimental technique to resolve the current distribution and an underpinning nonlinear percolation model, one relies on empirical rules and safety factors to engineer materials. We introduce Bose-Einstein condensate microscopy to address the longstanding problem of imaging active current flow in 2D materials. We report on performance improvement of this technique whereby observation of dynamic redistribution of current pathways becomes feasible. We show how this, combined with existing thermal imaging methods, eliminates the need for assumptions between electrical and thermal properties. This will enable testing and modeling individual junction behavior and hot-spot formation. Investigating both reversible and irreversible mechanisms will contribute to improved performance and reliability of devices.

Large area arrays of discrete single-molecule junctions derived from host-guest complexes.

The desire to continually reduce the lower limits of semiconductor integrated circuit (IC) fabrication methods continues to inspire interest in unimolecular electronics as a platform technology for the realization of future (opto)electronic devices. However, despite successes in developing methods for the construction and measurement of single-molecule and large-area molecular junctions, exercising control over the precise junction geometry remains a significant challenge. Here, host-guest complexes of the wire-like viologen derivative 1,1'-bis(4-(methylthio)-phenyl)-[4,4'-bipyridine]-1,1'-diium chloride ([1][Cl]2) and cucurbit[7]uril (CB[7]) have been self-assembled in a regular pattern over a gold substrate. Subsequently, ligandless gold nanoparticles (AuNPs) synthesized in situ are deposited over the host-guest array. The agreement between the conductance of individual mono-molecular junctions, appropriately chosen as a function of the AuNP diameter, within this array determined by conductive probe atomic force microscope (c-AFM) and true single-molecule measurements for a closely similar host-guest complex within a scanning tunneling microscope break-junction (STM-BJ) indicates the formation of molecular junctions derived from these host-guest complexes without deleterious intermolecular coupling effects.

Large‐Scale On‐Chip Integration of Gate‐Voltage Addressable Hybrid Superconductor–Semiconductor Quantum Wells Field Effect Nano‐Switch Arrays

AbstractStable, reproducible, scalable, addressable, and controllable hybrid superconductor–semiconductor (S–Sm) junctions and switches are key circuit elements and building blocks of gate‐based quantum processors. The electrostatic field effect produced by the split gate voltages facilitates the realization of nano‐switches that can control the conductance or current in the hybrid S–Sm circuits based on 2D semiconducting electron systems. Here, a novel realization of large‐scale scalable, and gate voltage controllable hybrid field effect quantum chips is experimentally demonstrated. Each chip contains arrays of split gate field effect hybrid junctions, that work as conductance switches, and are made from In0.75Ga0.25As quantum wells integrated with Nb superconducting electronic circuits. Each hybrid junction in the chip can be controlled and addressed through its corresponding source–drain and two global split gate contact pads that allow switching between their (super)conducting and insulating states. A total of 18 quantum chips are fabricated with 144 field effect hybrid Nb‐ In0.75Ga0.25As 2DEG‐Nb quantum wires and the electrical response, switching voltage (on/off) statistics, quantum yield, and reproducibility of several devices at cryogenic temperatures are investigated. The proposed integrated quantum device architecture allows control of individual junctions in a large array on a chip useful for emerging cryogenic quantum technologies.

Photoinduced Contact Evolution and Junction Rearrangement in Two‐Dimensional van der Waals Heterostructure

AbstractDevices based on 2DMs van der Waals (vdW) heterostructures always compose of multiple contacts. Due to the instability of nanoscale 2DMs and interfaces, these contacts can be affected by the operation‐induced photo or thermal effect. They can trigger the evolution of junctions and rearrange the junctions across a device, which are detrimental for applications. Herein, vdW heterostructure of indium selenide (InSe) and black phosphorus (BP) on Au electrodes are investigated to reveal the contact evolution and its relation to device performance. During operation, light irradiation changes the I–V characteristics from symmetry to strong rectification. Photocurrent mapping and Kelvin‐probe force microscopy (KPFM) reveal triple junctions in this heterostructure, i.e., Au‐InSe junction, InSe homojunction, and InSe‐BP heterojunction. The variation of I–V characteristics of vdW heterostructure is ascribed to the evolution of Au‐InSe junction from quasi‐ohmic junction with a near‐zero work function difference (Δφ) to a strong Schottky junction (Δφ = ≈0.27 eV). The stabilized device demonstrates distinguished time‐domain response at individual junctions and overall device, indicating the evolution of contacts and the consequent opposite junction directions degrade the overall device performance. This research emphasizes the importance of dealing with heterogeneous contacts and junction directions in designing vdW heterostructure photodetectors.

Harvesting and mapping ultrasonic vibration power using semiconducting wire-based tribovoltaic generators

Ultrasonic vibration is an excellent mechanical power source owing to its large power density. Harvesting ultrasonic vibrations has been demonstrated so far through piezoelectric effect, triboelectric effect, and electromagnetic induction. However, the majority of these devices only produce AC output which limits their potential applications. This work demonstrates, for the first time, the conversion of ultrasonic vibration power to DC output using semiconducting wire-based electric generators, in which one or several semiconductor wire/metal junction(s) are employed. A current density of up to 19 µA/cm2 and a peak power density of 5 µW/cm2 can be obtained under ultrasonic vibrations up to 37 kHz. The mapping of the ultrasonic vibrational strength has been achieved, demonstrating the capability of a self-driven powered ultrasonic sensor. The characteristics of individual semiconductor junctions and the series connection of several such junctions are studied using equivalent circuits.

The role of claudins in homeostasis.

Sequential expression of claudins, a family of tight junction proteins, along the nephron mirrors the sequential expression of ion channels and transporters. Only by the interplay of transcellular and paracellular transport can the kidney efficiently maintain electrolyte and water homeostasis in an organism. Although channel and transporter defects have long been known to perturb homeostasis, the contribution of individual tight junction proteins has been less clear. Over the past two decades, the regulation and dysregulation of claudins have been intensively studied in the gastrointestinal tract. Claudin expression patterns have, for instance, been found to be affected in infection and inflammation, or in cancer. In the kidney, a deeper understanding of the causes as well as the effects of claudin expression alterations is only just emerging. Little is known about hormonal control of the paracellular pathway along the nephron, effects of cytokines on renal claudin expression or relevance of changes in paracellular permeability to the outcome in any of the major kidney diseases. By summarizing current findings on the role of specific claudins in maintaining electrolyte and water homeostasis, this Review aims to stimulate investigations on claudins as prognostic markers or as druggable targets in kidney disease.

Mach–Zehnder-like interferometry with graphene nanoribbon networks

We study theoretically electron interference in a Mach–Zehnder-like geometry formed by four zigzag graphene nanoribbons arranged in parallel pairs, one on top of the other, such that they form intersection angles of 60∘. Depending on the interribbon separation, each intersection can be tuned to act either as an electron beam splitter or as a mirror, enabling tuneable circuitry with interfering pathways. Based on the mean-field Hubbard model and Green’s function techniques, we evaluate the electron transport properties of such eight-terminal devices and identify pairs of terminals that are subject to self-interference. We further show that the scattering matrix formalism in the approximation of independent scattering at the four individual junctions provides accurate results as compared with the Green’s function description, allowing for a simple interpretation of the interference process between two dominant pathways. This enables us to characterize the device sensitivity to phase shifts from an external magnetic flux according to the Aharonov–Bohm effect as well as from small geometric variations in the two path lengths. The proposed devices could find applications as magnetic field sensors and as detectors of phase shifts induced by local scatterers on the different segments, such as adsorbates, impurities or defects. The setup could also be used to create and study quantum entanglement.

A modeling framework to quantify the intermediate layer impact in III–V//Si multijunction solar cells

Multijunction solar cells (MJSCs) are capable of converting sunlight to electricity more efficiently than single-junction solar cells. The intermediate scattering layers between the individual junctions contribute to high efficiency by impacting the generated currents, photon recycling (PR), as well as luminescent coupling (LC) in the device. The MJSC efficiency can be simulated using expressions that involve a simplified and idealized intermediate layer structure but cannot accurately reflect its actual performance. This work, however, aims to establish a systematic optical model for MJSCs with complicated intermediate layers. It begins with incorporating the LC and PR effects into the developed model, emphasizing requirements for the cut-off wavelength and long-wavelength transmission of the intermediate layer. Furthermore, a three-dimensional metallic nanocylinder array is designed as the intermediate layer to improve device performance. With the model, high-performance MJSCs can be designed and optimised by quantifying the impact of PR and LC on device parameters.

Elucidating the Effects of Interconnecting Layer Thickness and Bandgap Variations on the Performance of Monolithic Perovskite/Silicon Tandem Solar Cell by wxAMPS.

In this study, we investigated the pathways for integration of perovskite and silicon solar cells through variation of the properties of the interconnecting layer (ICL). The user-friendly computer simulation software wxAMPS was used to conduct the investigation. The simulation started with numerical inspection of the individual single junction sub-cell, and this was followed by performing an electrical and optical evaluation of monolithic 2T tandem PSC/Si, with variation of the thickness and bandgap of the interconnecting layer. The electrical performance of the monolithic crystalline silicon and CH3NH3PbI3 perovskite tandem configuration was observed to be the best with the insertion of a 50 nm thick (Eg ≥ 2.25 eV) interconnecting layer, which directly contributed to the optimum optical absorption coverage. These design parameters improved the optical absorption and current matching, while also enhancing the electrical performance of the tandem solar cell, which benefited the photovoltaic aspects through lowering the parasitic loss.

Deformation tracking of truss lattices under dynamic loading based on Digital Image Correlation

Three-dimensional (3D) truss-based metamaterials (or architected materials) have been the subject of an increasing amount of studies, owing to their impressive and tunable mechanical properties. Unfortunately, experimentally studying their mechanical multiscale behavior under dynamic loading presents a challenge due to the complex time-dependent correlation between the overall truss response and the deformation of individual beams and beam junctions. Tracking the time-dependent deformation of 3D-printed low-density trusses is challenging for traditional techniques such as Digital Image Correlation (DIC), owing to the discrepancy between typical feature (strut) sizes and the field of few of the overall truss, further difficulty in applying speckle patterns, as well as the lack of a stable bright background during testing—especially when high rates and large 3D deformation are involved. As a remedy, we present an efficient DIC-based technique, which admits tracking the nodal displacements of points of interest (such as, e.g., the strut junctions) in periodic and non-periodic truss networks across a range of loading rates. We use this technique to identify the time-dependent nodal displacements of different truss architectures, whose large deformation is of interest for energy absorption capabilities of truss metamaterials. The quality of results is assessed by performing multiple trackings on each truss topology, which reveals that errors are negligible for the reported range of conditions.

Tonal noise case study: Locating the source of tones on HVAC equipment

The overall noise level measured from chiller units is controlled by primarily tonal noises from (1) the fans, (2) the compressors, and (3) the associated pipework. Three large chiller units were measured using AHRI 370 methodology to quantify the overall sound level spectra and A-weighted sound level from different chiller units in a range of environmental conditions. Whilst this method can identify a general area of tonal emission to within a couple of meters across a unit’s surface that is emitting discrete tonal noises, the method is limited when there are multiple potential tonal sources. Sound intensity imagery was used on two units to quantify the overall sound power emanating from the source, but also to offer a more advanced method of localizing the source of discrete tones to aid in the application of mitigation treatments. Results presented include visually displaying and quantifying the location of noise emission from fan blade pass frequencies and associated harmonics, localization of problematic tones emanating from individual pipework junctions and valves, and the reductions in sound power emissions achieved from lagging compressors and pipework.

The Reliability of SAC305 Individual Solder Joints during Creep–Fatigue Conditions at Room Temperature

The failure of one solder joint out of the hundreds of joints in a system compromises the reliability of the electronics assembly. Thermal cycling is a result of both creep–fatigue mechanisms working together. To better understand the failure process in thermal cycling, it is crucial to analyze both the effects of creep and fatigue mechanisms in a methodical manner. In this work, individual solder junctions are subjected to accelerated shear fatigue testing to investigate the effects of creep and fatigue on joint dependability at room temperature. A modified fixture is used to conduct fatigue tests on an Instron 5948 micromechanical tester. SAC305 joints with an OSP surface finish were cycled under stress control at first, and then the strain was maintained for a set amount of time. In this investigation, three stress amplitudes of 16, 20, and 24 MPa are used, together with varying residence periods of 0, 10, 60, and 180 s. The fatigue life of solder junctions is described for each testing condition using the two-parameter Weibull distribution. Additionally, as a function of stress amplitude and residence time, a dependability model is created. For each testing scenario, the progression of the stress–strain loops was studied. By quantifying relevant damage metrics, such as plastic work per cycle and plastic strain at various testing circumstances, the damage due to fatigue is distinguished from creep. To investigate the relationships between plastic work and plastic strain with fatigue life, the Coffin–Manson and Morrow Energy model is used. The results indicate that using greater stress magnitudes or longer dwell periods significantly shortens fatigue life and dramatically increases plastic work and plastic strain. The housing impact is significant; in some circumstances, testing with a longer dwelling period and lower stress amplitude resulted in more damage than testing with a shorter dwelling period and higher stress levels. When illustrating the fatigue behavior of solder junctions under various stress amplitudes or dwellings, the Coffin–Manson and Morrow Energy model were both useful. In the end, general reliability models are developed as functions of plastic work and plastic strain.

Nonlocal Long-Range Synchronization of Planar Josephson-Junction Arrays

We study arrays of planar $\mathrm{Nb}$ Josephson junctions with contacts to intermediate electrodes, which allow measurements of individual junctions and, thus, provide an insight into intricate array dynamics. We observe strong indications for array phase locking, despite a significant interjunction separation. Several unusual phenomena are reported, such as a bistable critical current with reentrant superconductivity upon switching of nearby junctions; and ``incorrect'' Shapiro steps, occurring at mixing frequencies between the external rf radiation and the internal Josephson frequency in nearby junctions. Our results reveal a surprisingly strong and long-range interjunction interaction, which is attributed to nonlocality of planar-junction electrodynamics, caused by the long-range spreading of stray electromagnetic fields. The nonlocality greatly enhances the high-frequency interjunction coupling and enables large-scale synchronization. Therefore, we conclude that planar geometry is advantageous for the realization of coherent Josephson electronics.